This proposal outlines a comprehensive plan for the principal investigator to develop a career studying the basis of mitochondria! disorders in children. The candidate is a Clinical Associate in Pediatrics at The Children's Hospital of Philadelphia (CHOP). His research will be mentored by Narayan Avadhani, PhD and Celeste Simon, PhD. His clinical mentor is Marc Yudkoff, MD, chief of the Division of Child Development, Rehabilitation Medicine and Metabolic Disease. The research and clinical environment provided by CHOP is uniquely suited towards the needs of the principal investigator due to its commitment to translational research and the presence of other physicians and scientists studying and treating mitochondrial disorders. The long term objective of the studies outlined in this proposal is the identification of the role of mitochondrial transcription in the pathogenesis of mitochondrial disease. In our first aim, we will study the production of mitochondrial mRNA using cells or cell extracts to determine the basic requirements for mitochondrial gene expression. In our second aim, we will specifically investigate the role of LRPPRC in mitochondrial transcription. This protein may regulate transcription, as it binds to a segment of the control region of mitochondrial DMA. The gene encoding LRPPRC is mutated in patients with French-Canadian Leigh Syndrome, and our studies will determine whether or not this particular pediatric mitochondrial disease is caused by a global defect in mitochondrial transcription. Finally, we propose to develop techniques for the analysis of transcriptional failure in patient-derived samples. This will allow us to study patients with mitochondrial failure who lack a specific diagnosis. The identification of patients with genetically-determined errors in mitochondrial transcription would both augment our understanding of the basic biology of the mitochondrion and improve patient care. The proposal overall advances the goal of studying biochemical processes and metabolism as these relate to brain functioning, injury and long term consequences to the brain.